1. Field of the Invention
The present invention relates to a method for manufacturing a hemisphere used in a hemispheric bearing apparatus. More particularly, the invention is directed to a method for manufacturing, capable for use in mass production and for enhancing the mechanical characteristic of a hemisphere, by manufacturing a sphere using a pair of forging frames, each formed in the shape of a hemisphere, grinding the spherical surface, and then dividing the sphere into two, thereby forming two hemispheres.
2. Description of the Related Art
Recently, with the improvement of technologies in the information and media industries, systems such as computer systems, audio systems, and video systems, are becoming more miniaturized. In this respect, there has been a trend to require components of such systems to have more precise performance. Driving apparatuses require a bearing which is precise, stable, and has a superhigh rotation performance. A hemispheric bearing, i.e., a dynamic pressure fluid bearing apparatus which supports both a radial load and a thrust load and is suitable to perform the superhigh speed rotation, has been actively developed.
FIG. 1 is a block diagram illustrating the processing order for manufacturing a hemispheric bearing using a NC (numerical control) machine tool and a CNC (computerized numerical control) machine tool.
First, the curvature and radius of the hemisphere, the position of a through hole, etc., are designed on paper (step 10). After performing a preliminary step for selecting a working position and tool, an instruction tape having the information about the hemisphere is made based on the designed drawing (step 20).
The information of the instruction tape is inputted to an information processing circuit which is a computerized numerical control apparatus of the CNC machine tool (step 30). By operating a servomechanism which controls the power and the position of the tool of the CNC machine, a test cutting of a material to be processed is performed (step 40). After that, in the case that the size of the hemisphere is within the allowable error as a result of a re-measurement, a hemisphere is manufactured by a machine tool (step 50).
When the hemisphere is completely manufactured (step 60), a through hole is formed so that the hemisphere 60 can be indented at a fixing axis 20, and the grinding and lapping process are performed (step 70) so that the sphericity of the hemisphere 60 can be within the allowable value. To control the clearance between the hemisphere and a bush by a spacer 40a, the upper end of the hemispheric surface of the hemisphere is cut in a predetermined length (step 80). After cutting, a dynamic pressure generating groove having a predetermined area is formed on the surface of the hemisphere, and then a surface treatment of the hemisphere is performed (step 90).
However, in the above mentioned case that the hemisphere of the hemispheric bearing is manufactured by a machine tool, first the hemisphere is manufactured by the machine tool and the through hole is formed so that the hemisphere can be indented in the fixing axis. After those steps, the methods for processing the hemispheric surface through grinding or lapping are adopted, and thereby manufacturing the hemispheric surface having the sphericity above 0.05 .mu.m is difficult due to time constraints. In other words, the conventional method of manufacturing requires too much time to process the hemispheres with precision, thereby it is difficult to achieve mass production.